Most common infections that occur during pregnancy, such as those of the skin and respiratory tract, cause no serious problems. However, some infections can be passed to the fetus before or during birth and damage the fetus or cause a miscarriage or premature birth.

Syphilis can be transmitted from a mother to the fetus through the placenta. Syphilis can cause several birth defects.

Human immunodeficiency virus (HIV) infection is transmitted to the fetus in about one fourth of pregnancies if women who have the infection are not treated. Experts recommend that women with HIV infection take one or more antiretroviral drugs during pregnancy. When pregnant women take zidovudine, the risk of transmitting HIV to the fetus is reduced to less than 8%. If women take several drugs, the risk can be reduced to as low as 1%. For some women with HIV infection, cesarean delivery, planned in advance, may further reduce the risk of transmitting HIV to the baby. Pregnancy does not seem to speed up the progression of HIV infection in women.

Genital herpes can be transmitted to the baby during a vaginal delivery. Babies who are infected with herpes can develop a life-threatening brain infection called herpes encephalitis. A herpes infection in babies can also damage other internal organs and cause skin and mouth sores, permanent brain damage, or even death. If women develop herpes sores in the genital area late in pregnancy or if herpes first develops during late pregnancy, women are usually advised to give birth by cesarean delivery, so that the virus is not transmitted to the baby. If no sores are present and herpes develops earlier, the risk of transmission is very low.

Infections that are not transmitted sexually and can cause problems include the following:

Cytomegalovirus infection can cross the placenta and damage the fetus’s liver and brain, and the fetus may not grow as much as expected.

Chickenpox (varicella) increases the risk of a miscarriage. It may damage the eyes of the fetus or cause defects of the limbs, blindness, or intellectual disability. The fetus’s head may be smaller than normal.

Toxoplasmosis, a protozoal infection, may cause a miscarriage, death of the fetus, and serious birth defects.

Listeriosis, a bacterial infection, increases the risk of a premature birth, miscarriage, and stillbirth. Newborns may have the infection, but symptoms may be delayed until several weeks after birth.

Bacterial infections of the vagina (such as bacterial vaginosis) may lead to preterm labor or premature rupture of the membranes containing the fetus.

Urinary tract infections increase the risk of preterm labor and premature rupture of the membranes containing the fetus.

Chronic viral hepatitis may be transmitted sexually or in other ways. It can increase the risk of premature birth.

Treatment

Sometimes drugs, depending on the balance of benefits and risks

To determine whether to treat pregnant women with antimicrobial drugs, doctors weigh the risks of using the drug against the risks of the infection. Some antibacterial drugs, such as the penicillins, cephalosporins, and drugs related to erythromycin (called macrolides), are generally considered safe for use during pregnancy. Other antibacterial drugs, including tetracyclines and fluoroquinolones, may cause problems in the fetus (see Table: Some Drugs That Can Cause Problems During Pregnancy*).

Doctors also consider whether treatment is likely to have any benefits. For example, if women have bacterial vaginosis but no symptoms and if the pregnancy is not considered high-risk, treating bacterial vaginosis is not known to have any benefits.

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